FIX: Update `optimization_tutorial.py` to expose `batch_size` in `train_loop()`

[loganthomas]

Description

batch_size is not currently exposed as train_loop() parameter

• Re-implements #2920 (accidental deletion from forked repo)

Checklist

• [X] The issue that is being fixed is referred in the description (see above "Fixes #ISSUE_NUMBER")
• [X] Only one issue is addressed in this pull request
• [X] Labels from the issue that this PR is fixing are added to this pull request
• [X] No unnecessary issues are included into this pull request.

cc @subramen @albanD @sekyondaMeta @svekars @kit1980 @brycebortree